The documents U.S. Publ. No. 2004/0067761 and U.S. Publ. No. 2006/2167849 propose exchanging messages between terminals after connection to an IP network and thus after recovery of their respective IP addresses in order to be able to request data call set-up via the IP network.
The documents WO2008/049647 and EP 1 555 786 teach setting-up a call between two terminals in an IP environment when the called party is not connected to the IP network. To this end, a terminal connected to the IP network requiring to call a destination terminal that is not connected to the IP network sends the destination terminal a message including its IP address via a network other than the IP network. This message commands the destination terminal to set-up a data call via the IP network with the terminal connected to the IP network. Because the terminal initiating the call does not set up the call, it is not identified as the calling terminal for the call. The destination terminal must be able to connect to the IP network to set up said call with the terminal connected to the IP network, the aim being to reduce failures to set up data calls in an IP network.
If the list of contacts is provided by a web server, the server then assumes responsibility for instigating the operations necessary for connecting a user terminal that sent a request to a terminal associated with the selected contact.
A first known technique connects the two terminals by means of a link conforming to the Internet Protocol (IP). This solution sets up a first communications link between the server receiving the call request and one of the two terminals and then a second link between the server and the other terminal, these two links thereafter being joined to set-up a single link between the two terminals via the server.
That technique has the drawback of being greedy for server resources, notably bandwidth. It is also applicable to packet-switched networks but not suitable for circuit-switched networks. In particular, it is not applicable to setting up a call between two terminals via a GSM mobile network.
Finally, because the call is set up from a network server, that technical solution gives rise to a billing problem in that for a call set up in circuit mode, it is usually the terminal sending the call request that is billed. That technique is thus incompatible with the billing method used in circuit-switched networks.
A need has therefore emerged for automated call set-up between two terminals that is applicable to circuit-switched networks, notably GSM mobile networks, and compatible with the billing mode used in those networks.